PROJECT SUMMARY Thalidomide and its analogs, lenalidomide and pomalidomide, have revolutionized the treatment of patients with multiple myeloma (MM) and other hematologic malignancies. However, therapeutic resistance still limits their efficacy and represents a critical unmet medical need. These drugs work through a unique mechanism leading to the targeted degradation of oncoproteins. Because only the protein levels of the drug targets are affected, they have been difficult to study using conventional technologies. We developed a novel targeted mass spectrometry assay to measure these proteins and now propose in Aim 1 to use this assay to study the relationship between the level of thalidomide analog targets and the development of lenalidomide resistance in patients. In an orthogonal study to identify mediators of thalidomide analog resistance downstream of substrate degradation I have performed multiple genetic screens in a MM cell line and have identified the retinoic acid receptor alpha and the nuclear corepressor as potential mediators of lenalidomide resistance. In Aim 2 I propose to further characterize these genes and their roll in mediating the response to thalidomide analogs in MM cells. Collectively, this work will further outline two major pathways of resistance to a clinically important class of drugs and shed new light on methods to overcome resistance. The applicant, Dr. Adam Sperling, is an oncologist at the Dana-Farber Cancer Institute (DFCI). He spends 80% of his time in translational research and 20% in clinical practice caring for patients with cancer. He has outlined a five-year career development plan to meet his goal of becoming an independent investigator in translational research. Dr. Sperling has assembled an Advisory Committee of internationally recognized experts to provide scientific and career mentorship. He has established collaborations with experts in cancer epigenetics, mass spectrometry, and applied biostatistics to provide experimental advice and specific training in the field. Dr. Sperling will conduct this research at the DFCI and leverage the exceptional research and teaching environment at the DFCI, Harvard, and the Broad Institute. The Dana-Farber Cancer Institute, which harbors an outstanding research community and has a long track record for successful mentorship of independent physician scientists, is an ideal environment for completion of these experiments and the realization of Dr. Sperling?s long-term career goal of being an independent physician- scientist.